Downlink signal receiving method, terminal, and source base station

ABSTRACT

This application provides a downlink signal receiving method, a terminal, and a source base station. The method includes: A terminal may receive downlink signals from a source base station and a target base station in a handover process. When receiving no downlink signal from the target base station, the terminal receives the downlink signal only from the source base station. In addition, after handover is completed, the terminal receives the downlink signal only from the target base station, so that the terminal can still receive the downlink signal from the source base station in the handover process. Therefore, downlink signal transmission interruption caused by the handover process may be reduced to 0 ms or nearly 0 ms. In other words, zero interruption or nearly zero interruption of data transmission may be implemented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2018/118722, filed on Nov. 30, 2018, the disclosure of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

This application relates to the field of communications technologies,and in particular, to a downlink signal receiving method, a terminal,and a source base station.

BACKGROUND

When a terminal moves from a cell (source cell) to another cell (atarget cell), a handover procedure may be triggered. In a time periodfrom handover start to handover completion, the terminal no longerreceives a downlink signal from the source cell, and the terminal doesnot receive a downlink signal from the target cell. Consequently,downlink signal transmission is interrupted.

However, with an increase in service types, a sharp increase in servicedata volume, and an increase in a moving speed of a terminal,requirements on service interruption time and reliability in a handoverprocess are increasingly strict. For example, mobile office, mobilevideo services, vehicle wireless control, train wireless control, andthe like require zero or nearly zero service interruption.

Therefore, downlink signal transmission interruption in the handoverprocess is a problem that urgently needs to be resolved currently.

SUMMARY

This application provides a downlink signal receiving method, aterminal, and a source base station, to resolve a problem of downlinksignal transmission interruption in a handover process.

According to a first aspect, this application provides a downlink signalreceiving method, applied to a process in which a terminal is handedover from a source base station to a target base station, where themethod includes: The terminal receives a first message from the sourcebase station, where the first message includes a first indication, andthe first indication is used to indicate the terminal to receivedownlink signals on a same frequency, in other words, indicate toreceive downlink signals from the source base station and the targetbase station on a same carrier frequency. The terminal receives thedownlink signals from the source base station and the target basestation based on the first indication.

Based on this solution, the terminal may receive the downlink signalsfrom the source base station and the target base station in a handoverprocess. For example, when the terminal needs to receive the downlinksignal from the target base station while receiving the downlink signalfrom the source base station in the handover process, the terminalreceives the downlink signals from the source base station and thetarget base station. When receiving no downlink signal from the targetbase station, the terminal receives the downlink signal (where thedownlink signal carries downlink data) only from the source basestation. In addition, after handover is completed, the terminal receivesthe downlink signal (where the downlink signal carries downlink data)only from the target base station, so that the terminal can stillreceive the downlink signal from the source base station in the handoverprocess. Therefore, downlink signal transmission interruption caused bythe handover process may be reduced to 0 ms or nearly 0 ms. In otherwords, zero interruption or nearly zero interruption of datatransmission may be implemented.

In a possible implementation, that the terminal receives the downlinksignals from the source base station and the target base station basedon the first indication includes: The terminal configures at least twoprocessing resources based on the first indication, where one processingresource includes a baseband resource and a fast Fourier transformationFFT, and at least two processing resources correspond to a same carrierfrequency. The terminal receives the downlink signal from the sourcebase station by using a first processing resource in the at least twoprocessing resources. The terminal receives the downlink signal from thetarget base station by using a second processing resource in the atleast two processing resources, where the first processing resource isdifferent from the second processing resource.

In a possible implementation, if the terminal has a carrier aggregationcapability, a bandwidth of a baseband resource included in the firstprocessing resource is the same as a bandwidth of a baseband resourceincluded in the second processing resource, and a size of an FFTcorresponding to the first processing resource is the same as a size ofan FFT corresponding to the second processing resource. Alternatively,if the terminal does not have a carrier aggregation capability, abandwidth of a baseband resource included in the second processingresource is less than or equal to a bandwidth of a baseband resourceincluded in the first processing resource, and a size of an FFTcorresponding to the second processing resource is less than or equal toa size of an FFT corresponding to the first processing resource, wherethe bandwidth of the baseband resource included in the second processingresource is less than or equal to a preset bandwidth threshold.

In a possible implementation, the terminal sends a first capabilityindication to the source base station, where the first capabilityindication is used to indicate that the terminal has an intra-frequencyreceiving capability.

In a possible implementation, the terminal does not adjust an automaticgain control AGC gain based on the first indication. Alternatively, thefirst message further includes a second indication, and the terminaldoes not adjust an AGC gain based on the second indication.

In a possible implementation, the terminal sends a second capabilityindication to the source base station, where the second capabilityindication is used to indicate that the terminal has a capability of notadjusting the AGC gain.

In a possible implementation, the first indication is further used toindicate a fading margin, and the terminal sets a fixed AGC gain basedon the fading margin.

Alternatively, the terminal sets a fixed AGC gain based on a fadingmargin, where the first message further includes a third indication, andthe third indication is used to indicate the fading margin.

In a possible implementation, the terminal sends a third capabilityindication to the source base station, where the third capabilityindication is used to indicate that the terminal has a capability ofsetting the fixed AGC gain based on the fading margin.

In a possible implementation, the first message further includes a starttime point. That the terminal receives the downlink signals from thesource base station and the target base station based on the firstindication includes: The terminal starts to receive, at the start timepoint, the downlink signals from the source base station and the targetbase station based on the first indication.

In a possible implementation, the first message further includes an endtime point, and the terminal stops, at the end time point, receiving thedownlink signals from the source base station and the target basestation.

Alternatively, the first message further includes first duration. Afterthe first duration from the start time point, the terminal stopsreceiving the downlink signals from the source base station and thetarget base station.

In a possible implementation, the first message is a radio resourcecontrol RRC connection reconfiguration message.

According to a second aspect, this application provides a downlinksignal receiving method, applied to a process in which a terminal ishanded over from a source base station to a target base station, wherethe method includes: The source base station generates a first message,where the first message includes a first indication, and the firstindication is used to indicate the terminal to receive downlink signalson a same frequency, in other words, indicate to receive downlinksignals from the source base station and the target base station on asame carrier frequency. The source base station sends the first messageto the terminal.

Based on this solution, the terminal may receive the downlink signalsfrom the source base station and the target base station in a handoverprocess. For example, when the terminal needs to receive the downlinksignal from the target base station while receiving the downlink signalfrom the source base station in the handover process, the terminalreceives the downlink signals from the source base station and thetarget base station. When receiving no downlink signal from the targetbase station, the terminal receives the downlink signal (where thedownlink signal carries downlink data) only from the source basestation. In addition, after handover is completed, the terminal receivesthe downlink signal (where the downlink signal carries downlink data)only from the target base station, so that the terminal can stillreceive the downlink signal from the source base station in the handoverprocess. Therefore, downlink signal transmission interruption caused bythe handover process may be reduced to 0 ms or nearly 0 ms. In otherwords, zero interruption or nearly zero interruption of datatransmission may be implemented.

In a possible implementation, the source base station receives a firstcapability indication from the terminal, where the first capabilityindication is used to indicate that the terminal has an intra-frequencyreceiving capability.

In a possible implementation, the first indication is further used toindicate the terminal not to adjust an AGC gain, or the first messagefurther includes a second indication, and the second indication is usedto indicate the terminal not to adjust an AGC gain.

In a possible implementation, the source base station receives a secondcapability indication from the terminal, where the second capabilityindication is used to indicate that the terminal has a capability of notadjusting the AGC gain.

In a possible implementation, the first indication is further used toindicate a fading margin. In this way, the terminal can set a fixed AGCgain based on the fading margin. Alternatively, the first messagefurther includes a third indication, and the third indication is used toindicate a fading margin, so that the terminal may set a fixed AGC gainbased on the fading margin.

In a possible implementation, the source base station receives a thirdcapability indication from the terminal, where the third capabilityindication is used to indicate that the terminal has a capability ofsetting the fixed AGC gain based on the fading margin.

In a possible implementation, the first message further includes a starttime point, so that the terminal may start, at the start time point, toreceive the downlink signals from the source base station and the targetbase station based on the first indication.

In a possible implementation, the first message further includes an endtime point, so that the terminal can stop, at the end time point,receiving the downlink signals from the source base station and thetarget base station. Alternatively, the first message further includesfirst duration, so that after the first duration from the start timepoint, the terminal can stop receiving the downlink signals from thesource base station and the target base station.

In a possible implementation, the first message is a radio resourcecontrol RRC connection reconfiguration message.

According to a third aspect, this application provides a communicationsapparatus. The communications apparatus has a function of implementingthe terminal or the access network device in the foregoing methodembodiments. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor the software includes one or more units or modules corresponding tothe foregoing function.

In a possible design, the communications apparatus includes a processor,a memory, a bus, and a communications interface, where the memory storescomputer-executable instructions, the processor is connected to thememory through the bus, and when the communications apparatus runs, theprocessor executes the computer-executable instructions stored in thememory; so that the communications apparatus performs the downlinksignal receiving method according to any one of the first aspect or theimplementations of the first aspect, or performs the downlink signalreceiving method according to any one of the second aspect or theimplementations of the second aspect. For example, the communicationsapparatus may be a terminal, a base station, or the like.

In another possible design, the communications apparatus mayalternatively be a chip, for example, a chip of a terminal or a chip ofa source base station. The chip includes a processing unit, andoptionally, further includes a storage unit. The chip may be configuredto perform the downlink signal receiving method according to any one ofthe first aspect or the implementations of the first aspect, or performthe downlink signal receiving method according to any one of the secondaspect or the implementations of the second aspect.

According to a fourth aspect, this application provides a computerstorage medium, storing computer software instructions used by theforegoing terminal, where the computer software instructions include aprogram designed to perform any one of the foregoing aspects.

According to a fifth aspect, this application provides a computerprogram product. The computer program product includes computer softwareinstructions, where the computer software instructions may be loaded byusing a processor to implement the procedure of the downlink signalreceiving method in any one of the foregoing aspects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic diagram of a possible application scenarioaccording to this application;

FIG. 1B is a schematic diagram of a possible application scenarioaccording to this application;

FIG. 2 is a schematic diagram of a downlink signal receiving methodaccording to this application;

FIG. 3 is a schematic diagram of a processing resource allocation methodaccording to this application when a terminal has a carrier aggregationcapability;

FIG. 4 is a schematic diagram of a processing resource allocation methodaccording to this application when a terminal does not have a carrieraggregation capability;

FIG. 5 is a schematic diagram of an apparatus according to thisapplication; and

FIG. 6 is a schematic diagram of another apparatus according to thisapplication.

DESCRIPTION OF EMBODIMENTS

Abase station includes but is not limited to a BBU, a transmissionreception point (TRP), a transmission point (TP), a mobile switchingcenter, and the like.

It should be noted that in this application, a “handover” scenariosometimes means that a terminal is handed over from a source cell to atarget cell, or sometimes means that a terminal is handed over from asource base station to a target base station. The two cases have a samemeaning, and are alternately used in this application. This is centrallydescribed herein. In addition, in this application, the “handover”scenario sometimes means that the terminal receives information (forexample, a downlink signal) from the source base station/target basestation, and the terminal sends information (for example, an uplinksignal) to the source base station/target base station, or sometimesmeans that the terminal receives information (for example, a downlinksignal) from the source cell/target cell, and the terminal sendsinformation (for example, an uplink signal) to the source cell/thetarget cell. The two cases have a same meaning, and are alternately usedin this application. This is centrally described herein.

That is, in this application, the source base station and the sourcecell have a same meaning, and the target base station and the targetcell have a same meaning.

With an increase in service types, a sharp increase in service datavolume, and an increase in a moving speed of the terminal, requirementson service interruption time and reliability in a handover process areincreasingly strict. For example, mobile office, mobile video services,vehicle wireless control, train wireless control, and the like requirezero interruption in service transmission.

In a conventional technology, in a procedure in which the terminal ishanded over from the source base station to the target base station,after receiving a handover command (HO command) from the source basestation, the terminal stops sending information on an uplink (UL) to thesource base station, starts to search for the target base station, andsynchronizes time and frequency with the target base station. Then, theterminal initiates a random access process to the target base station.In the random access process, the terminal first obtains an occasion atwhich the terminal sends a random access preamble to the target basestation, in other words, an occasion of a physical random access channel(PRACH). When the occasion arrives, the terminal sends the Preamble(which is denoted as Message1, Msg1 for short) to the target basestation. Then, the terminal monitors a physical downlink control channel(PDCCH) scrambled by using a random access radio network temporaryidentifier (RA-RNTI), where the PDCCH is used to schedule a randomaccess response (RAR) message (which is denoted as Message2, Msg2 forshort). The RAR message includes uplink timing advance (TA) and anuplink resource grant (UL grant). Finally, the terminal sends a handovercomplete (HO complete) message (which is denoted as Message3, Msg3 forshort) to the target base station by using the UL grant and the TA. Thehandover command may be mobility control information, and is included ina radio resource control (RRC) connection reconfiguration message. Thehandover complete message may be an RRC connection reconfigurationcomplete message.

In the foregoing process in which the terminal is handed over from thesource base station to the target base station, after receiving thehandover command from the source base station, the terminal needs toprocess the command, and then stops sending an uplink signal to thesource base station and stops receiving a downlink signal from thesource base station. If the terminal has detected the target cell, andhas information such as time synchronization and a cell identifier (cellID) of the target cell, the terminal does not need to perform cellsearch including synchronization again. If the terminal does not havethe foregoing information of the target cell, or the foregoinginformation had by the terminal is invalid, the terminal needs toperform cell search again. The terminal also needs to complete accuratetime and frequency synchronization with the target cell, that is, thefine synchronization. In addition, the terminal further needs to updaterelated configuration information of a media access control (MAC) layerand a higher layer, and is ready to receive a signal from the targetbase station. In a scenario in which a random access channel (RACH)procedure needs to be performed, the terminal initiates a RACH process.After receiving the Msg3, the terminal may start to send an uplinksignal to the target base station, and receive a downlink signal fromthe target base station.

In the foregoing processes, processing of the handover command, the cellsearch, fine synchronization, update of MAC layer/higher layerparameters, and the RACH process cause transmission interruption of theuplink and downlink signals. That is, data transmission interruption ina cell handover process is caused. To be specific, in a time period fromhandover start to handover completion, the terminal no longer sends theuplink signal to the source base station, and does not receive thedownlink signal from the source base station. In addition, the terminalneither sends an uplink signal to the target base station, nor receivesa downlink signal from the target base station. The data transmissioninterruption includes uplink signal transmission interruption anddownlink signal transmission interruption.

To resolve the foregoing problem of downlink signal transmissioninterruption, the 3rd generation partnership project (3GPP) Rel-14proposes a handover time shortening technology (for example, amake-before-break technology or an RACH-less technology). According tothe 3GPP protocol 36.133, an interruption time period caused by thetechnology is still up to 5 ms. In other words, this technology cannotwell solve the problem of downlink signal transmission interruption. Inaddition, this technology does not resolve interruption caused by thefine synchronization.

In addition, the RACH-less technology in the handover time shorteningtechnology has a limitation: The technology requires that the sourcecell and the target cell need to be synchronized, in other words, asubframe boundary delay difference between the source cell and thetarget cell is fixed and less than a specific value, for example, 3microseconds (μs). When this technology is used, the terminal sends asignal to the source cell and the target cell by using a same TA. Such arequirement is not applicable to a typical long term evolution (LTE)frequency division duplex (FDD) asynchronous deployment scenario,another FDD deployment scenario, or a synchronization scenario in whicha delay difference is relatively large.

It should be noted that, in this application, the uplink signal includesbut is not limited to uplink data, uplink signaling, an uplink message,and an uplink feedback for a downlink signal. The downlink signalincludes but is not limited to: downlink data, downlink signaling, adownlink message, and a downlink feedback for an uplink signal.

To resolve the problem of downlink signal transmission interruptioncaused by the handover process in the conventional technology, as shownin FIG. 2, this application provides a downlink signal receiving method.The method includes the following steps.

Step 201: A source base station sends a first message to a terminal.Correspondingly, the terminal may receive the first message.

The first message includes a first indication. The first indication isused to indicate the terminal to receive downlink signals on a samefrequency. To be specific, the first indication is used to indicate theterminal to receive downlink signals from the source base station and atarget base station on a same carrier frequency.

Optionally, the first message may be a radio resource control RRC)connection reconfiguration message.

Step 202: The terminal receives the downlink signals from the sourcebase station and the target base station based on the first indication.

After receiving the first indication, the terminal may directlyconfigure a bearer on a target base station side, and monitor downlinkcontrol information (DCI), to receive the downlink signal from thetarget base station.

Based on this method, the terminal may receive the downlink signals fromthe source base station and the target base station in a handoverprocess. For example, when the terminal needs to receive the downlinksignal from the target base station while receiving the downlink signalfrom the source base station in the handover process, the terminalreceives the downlink signals from the source base station and thetarget base station. When receiving no downlink signal from the targetbase station, the terminal receives the downlink signal (where thedownlink signal carries downlink data) only from the source basestation. In addition, after handover is completed, the terminal receivesthe downlink signal (where the downlink signal carries downlink data)only from the target base station, so that the terminal can stillreceive the downlink signal from the source base station in the handoverprocess. Therefore, downlink signal transmission interruption caused bythe handover process may be reduced to 0 ms or nearly 0 ms. In otherwords, zero interruption or nearly zero interruption may be implemented.

In an implementation, the terminal may further send a first capabilityindication to the source base station, where the first capabilityindication is used to indicate that the terminal has an intra-frequencyreceiving capability. Based on the method, the source base stationlearns that the terminal has the intra-frequency receiving capability,so that the source base station may indicate, according to the foregoingstep 201, the terminal to perform intra-frequency receiving.

In an implementation, the source base station may further send a fifthcapability indication or a first permission indication to the terminal,where the indication is used to indicate that the source base stationsupports the terminal having the intra-frequency receiving capability inperforming the intra-frequency receiving or allows the terminal havingthe intra-frequency receiving capability to perform the intra-frequencyreceiving.

In an implementation, the first message in step 201 may further includea start time point. In this case, in step 201, the terminal starts, atthe start time point, to receive the downlink signals from the sourcebase station and the target base station based on the first indication.For example, the start time point may indicate an L^(th) symbol of anN^(th) subframe of an M^(th) system frame that uses a time point of thesource base station as a reference, where M, N, and L are integersgreater than or equal to 0.

In an implementation, the first message in step 201 may further includean end time point, and the terminal stops, at the end time point,receiving the downlink signals from the source base station and thetarget base station. Alternatively, the first message includes firstduration. After the first duration from the start time point, theterminal stops receiving the downlink signals from the source basestation and the target base station.

In an implementation, in step 202, that the terminal receives thedownlink signals from the source base station and the target basestation based on the first indication specifically includes: Theterminal configures at least two processing resources based on the firstindication, where one processing resource includes a baseband resourceand a fast Fourier transformation (FFT), and the at least two processingresources correspond to a same carrier frequency. The terminal receivesthe downlink signal from the source base station by using a firstprocessing resource in the at least two processing resources, andreceives the downlink signal from the target base station by using asecond processing resource in the at least two processing resources,where the first processing resource is different from the secondprocessing resource. Based on the method, the at least two processingresources are configured for the terminal, where the first processingresource may be used to receive the downlink signal from the source basestation, and the second processing resource may be used to receive thedownlink signal from the target base station. This implements receivingof the downlink signals from the source base station and the target basestation.

With reference to FIG. 3 and FIG. 4, the following uses an example todescribe a specific implementation of allocating processing resources.

FIG. 3 is a schematic diagram of a processing resource allocation methodused when a terminal has a carrier aggregation (CA) capability. If theterminal has the carrier aggregation capability, a bandwidth of abaseband resource included in the first processing resource may be thesame as a bandwidth of a baseband resource included in the secondprocessing resource, and a size of an FFT corresponding to the firstprocessing resource is the same as a size of an FFT corresponding to thesecond processing resource.

The terminal having the carrier aggregation capability refers to aterminal that can support carrier aggregation. In a downlink, theterminal having the carrier aggregation capability can receive signalson different carriers. Therefore, the terminal includes a plurality ofprocessing resources, where one processing resource includes an FFT anda baseband resource.

A plurality of processing resources may be configured for each receiveantenna of the terminal. For example, if the terminal has two receiveantennas (in other words, two receive antennas), configuring at leasttwo processing resources means that one or more additional processingresources are added when one processing resource exists, that is, atleast two processing resources need to be configured for each antenna.That each receive antenna is configured with two processing resources isused as an example. Referring to FIG. 3, each receive antenna iscurrently configured with one processing resource (including a2048-point FFT and a baseband resource), and configuring two processingresources means that another processing resource is configured, wherethe another processing resource includes a 2048-point FFT and a basebandresource. In addition, the originally configured processing resource isused to receive a downlink signal of a source cell, and the additionalprocessing resource is used to receive a downlink signal of a targetcell. Alternatively, the originally configured processing resource isused to receive a downlink signal of a target cell, and the additionalprocessing resource is used to receive a downlink signal of a sourcecell.

It should be noted that this solution is different from typical carrieraggregation. In typical carrier aggregation, a plurality of processingresources on a terminal correspond to different carrier frequencies, andthese carriers are in different bands (band). However, in this solution,the plurality of processing resources correspond to a same carrierfrequency. Therefore, the plurality of processing resources share a sameradio frequency chain. As shown in FIG. 4, the radio frequency chainincludes, but is not limited to, a duplexer, a low noise amplifier(LNA), a filter, a down converter, and an analog-digital converter(ADC). The two processing resources shown in FIG. 3 share the radiofrequency chain. In addition, status update of the radio frequency chainaffects receiving of the downlink signals of the source cell and thetarget cell by the terminal.

FIG. 4 is a schematic diagram of a processing resource allocation methodused when a terminal does not have a carrier aggregation capability. Fora terminal that does not have a carrier aggregation capability, toreduce costs and complexity of the terminal, low-cost asymmetric dualFFT may be designed, in other words, an additional processing resourceis added. The processing resource includes a small-point FFT and abaseband resource.

In an implementation, when the terminal does not have the carrieraggregation capability, a bandwidth of a baseband resource included inthe second processing resource is less than or equal to a bandwidth of abaseband resource included in the first processing resource, and a sizeof an FFT corresponding to the second processing resource is less thanor equal to a size of an FFT corresponding to the first processingresource, where the bandwidth of the baseband resource included in thesecond processing resource is less than or equal to a preset bandwidththreshold. For example, referring to FIG. 4, each receive antenna of theterminal currently has one processing resource (in other words, thefirst processing resource), and then an additional processing resource(in other words, the baseband resource included in the second processingresource) of 5 MHz or 10 MHz is added for each receive antenna, wherethe preset bandwidth threshold is greater than or equal to 5 MHz, orgreater than or equal to 10 MHz. The second processing resource supportstime and frequency synchronization and power delay profile (PDP)estimation in a target cell, and information obtained by using thesecond processing resource may be shared with the FFT (which may bereferred to as a primary FFT) corresponding to the first processingresource, so that the primary FFT can receive a downlink signal of thetarget cell. In addition, the size (a 1024-point FFT or a 512-point FFTin FIG. 4) of the FFT corresponding to the second processing resource isless than the size (a 2048-point FFT in FIG. 4) of the FFT correspondingto the first processing resource. When the size of the FFT correspondingto the second processing resource is less than the size of the FFTcorresponding to the first processing resource, an additional filterneeds to be added before the FFT corresponding to the second processingresource.

Because the size of the FFT corresponding to the first processingresource is different from the size of the FFT (which may be referred toas a secondary FFT) corresponding to the second processing resource,when the terminal receives signals from a source cell and the targetcell, a bandwidth range in which the terminal works in the target cellneeds to be limited. For example, a Msg2 scheduling resource may belimited. To be specific, scheduling of the Msg2 is performed within 5MHz or 10 MHz. In a time period in which downlink signals are sent fromthe source cell and the target cell, a scheduling resource for datatransmission in the target cell may be limited. For example, schedulingis performed within 5 MHz or 10 MHz.

In a possible implementation, a bandwidth of a PDCCH for scheduling aphysical downlink shared channel (PDSCH) that carries the Msg2 may be asystem bandwidth, and a bandwidth of the PDSCH used to send the Msg2 maybe the foregoing 5 MHz or 10 MHz. Optionally, if the size of the FFTcorresponding to the second processing resource is less than the size ofthe FFT corresponding to the first processing resource, before theterminal receives, from the target cell, the PDCCH that schedules theMsg2, the terminal receives, by using the FFT corresponding to the firstprocessing resource, the PDCCH that schedules the Msg2.

In a possible implementation, the terminal selects a preamble from afirst preamble set and sends the preamble to the target cell, where thefirst preamble set is used for a terminal that supports a small-pointFFT.

In a possible implementation, the target cell indicates, to the terminalby using the source cell, a bandwidth or a resource set of the PDCCHthat schedules the Msg2, and the terminal receives, on the indicatedbandwidth or resource set, the PDCCH that schedules the Msg2.

It should be noted that in a new radio (NR) system, a minimum cellsystem bandwidth is 100 M. However, due to a limitation of a terminalcapability and consideration of terminal power consumption, a concept ofa bandwidth part (BWP) is introduced, and a terminal can work only in aspecific bandwidth. When handover is performed between NR base stations,it is difficult for the terminal to have a capability of receiving thedownlink signals of the source cell and the target cell. Therefore, aproblem of data transmission interruption may be resolved by using themethod in the embodiment shown in FIG. 4. A specific implementation isas follows. The terminal reports an asymmetric FFT capability. NR isused as an example for description, for example, a primary FFT is a4096-point FFT, and a secondary FFT is a 1024-point FFT. When theterminal receives the downlink signals of the source cell and the targetcell, a bandwidth range in which the terminal receives data in thetarget cell or a new secondary cell may be limited.

Optionally, when reporting the asymmetric FFT capability, the terminalmay report some or all of the following information: a size of theprimary FFT and a size of the secondary FFT, a bandwidth that supportsreceiving a signal of the secondary cell, a bandwidth for receiving asignal of the target cell during handover, and the like.

In still another implementation, when the terminal does not have acarrier aggregation capability, an implementation similar to that shownin FIG. 3 may also be used to additionally add at least one sameprocessing resource (in other words, the second processing resource),where the processing resource includes an FFT and a baseband resourcethat are same as an FFT and a baseband resource that are included in acurrent processing resource (in other words, the first processingresource) of an antenna of the terminal. The second processing resourcesupports time and frequency synchronization and PDP estimation in thetarget cell, and information obtained by using the second processingresource may be shared with the FFT (which may be referred to as aprimary FFT) corresponding to the first processing resource, so that theprimary FFT can receive a downlink signal of the target cell.

In addition, in mobile communications, because a quantity of ADCquantization bits is limited, a received signal needs to be amplified orattenuated to a specific amplitude that is suitable for ADCquantization. Because of a fading change of a channel, an amplitude of asignal received by the terminal through the channel changes with time.Therefore, on a receiver side, there is a function unit called automaticgain control (AGC). A function of the function unit is measuring a totalamplitude of the received signal, and continuously adjusting a multipleof a gain over time, so that an amplitude of a signal that reaches anADC through a radio frequency link falls within a proper input levelrange of the ADC. The gain adjustment is completed at a specific timepoint. Usually, the time point is determined by using a boundary of aframe, a subframe, or a symbol of a source cell as a reference.

FIG. 3 is used as an example. It is assumed that signals that arrive atthe terminal from the source cell and the target cell are notsynchronous, or a synchronization delay difference is relatively large,for example, greater than a length of one cyclic prefix (CP). When theterminal performs AGC adjustment based on the boundary of the frame, thesubframe, or the symbol of the source cell, for the target cell, asignal amplitude change occurs in an orthogonal frequency divisionmultiplexing (OFDM) symbol. For the OFDM symbol, amplitudes of receivedsignals before and after the AGC adjustment are greatly different.Consequently, a decoding error may occur after FFT is performed.Especially, when the affected OFDM symbol includes a cell-specificreference signal (CRS), the impact is greater.

To resolve the foregoing problem, in this application, in a time periodin which the foregoing problem may occur, the terminal may avoidadjusting an AGC gain, or reduce a frequency of adjusting an AGC gain.

In an implementation, the first indication included in the first messagein step 201 is further used to indicate not to adjust the AGC gain. Inthis case, the terminal may not adjust the AGC gain based on the firstindication. Alternatively, the first message in step 201 furtherincludes a second indication, and the second indication is used toindicate not to adjust the AGC gain. In this case, the terminal may notadjust the AGC gain based on the second indication. Optionally, theterminal may further send a second capability indication to the sourcebase station, where the second capability indication is used to indicatethat the terminal has a capability of not adjusting the AGC gain.

It should be noted that, if the first message includes a start timepoint, the terminal may not adjust the AGC gain from the start timepoint. If the first message includes an end time point or firstduration, the terminal may stop, after the end time point or the firstduration from the start time point, not adjusting the AGC gain, that is,may start to adjust the AGC gain in an original manner.

In still another implementation, the first indication is further used toindicate a fading margin, and the terminal sets a fixed AGC gain basedon the fading margin. Alternatively, the first message further includesa third indication, the third indication is used to indicate a fadingmargin, and the terminal sets a fixed AGC gain based on the fadingmargin. Optionally, the terminal may further send a third capabilityindication to the source base station, where the third capabilityindication is used to indicate that the terminal has a capability ofsetting the fixed AGC gain based on the fading margin.

It should be noted that, if the first message includes a start timepoint, the terminal may set the fixed AGC gain based on the fadingmargin from the start time point. If the first message includes an endtime point or first duration, the terminal may stop, after the end timepoint or the first duration from the start time point, setting the fixedAGC gain based on the fading margin, that is, may start to adjust theAGC gain in an original manner.

In an implementation, before step 201, the terminal may further send afourth capability indication to the source base station, where thefourth capability indication is used to indicate that the terminal has acapability of sending a preamble to the target base station after secondduration after the terminal device receives a handover command (wherethe handover command is carried in the first message). Alternatively,the fourth capability indication is used to indicate a value of thesecond duration, and the second duration is a time period in which theterminal processes the handover command. Further, the source basestation may send the fourth capability indication to the target basestation, so that the target base station can know when to start to sendthe downlink signal to the terminal.

It should be noted that “first”, “second”, “third”, “fourth”, and“fifth” in this application are only used to distinguish betweendifferent nouns, and do not constitute a limitation on meanings of thenouns.

It may be understood that, in the foregoing method embodiment, themethod implemented by the terminal may also be implemented by acomponent (for example, a chip or a circuit) that can be used in theterminal. This is not limited in this embodiment of this application.

Optionally, the first message may further include a power differenceindication, used to indicate a power difference for scheduling downlinkdata transmission between the source base station and the target basestation, to assist the terminal in using an advanced receiver.

FIG. 5 is a possible example block diagram of an apparatus according toan embodiment of the present invention. The apparatus 500 may exist in aform of software or hardware. The apparatus 500 may include a processingunit 502 and a communications unit 503. In an implementation, thecommunications unit 503 may include a receiving unit and a sending unit.The processing unit 502 is configured to control and manage an action ofthe apparatus 500. The communications unit 503 is configured to supportcommunication between the apparatus 500 and another network entity. Theapparatus 500 may further include a storage unit 501, configured tostore program code and data of the apparatus 500.

The processing unit 502 may be a processor or a controller, for example,may be a general-purpose central processing unit (CPU), ageneral-purpose processor, a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a field programmablegate array (FPGA) or another programmable logic device, a transistorlogic device, a hardware component, or any combination thereof. Theprocessing unit 502 may implement or execute various example logicalblocks, modules, and circuits described with reference to contentdisclosed in the present invention. The processor may be a combinationof processors implementing a computing function, for example, acombination of one or more microprocessors, or a combination of the DSPand a microprocessor. The communications unit 503 may be acommunications interface, a transceiver, a transceiver circuit, or thelike, where the communications interface is a general name, and mayinclude a plurality of interfaces during specific implementation. Thestorage unit 501 may be a memory.

In an embodiment, the apparatus 500 may be a terminal, or may be a chipin a terminal. The terminal may be configured to implement operationsperformed by the terminal in the foregoing embodiments. Specifically,for example, the communications unit 503 includes the sending unit andthe receiving unit. The receiving unit is configured to receive a firstmessage from the source base station, where the first message includes afirst indication, and the first indication is used to indicate theterminal to receive downlink signals from the source base station andthe target base station on a same carrier frequency. The processing unitis configured to receive the downlink signals from the source basestation and the target base station based on the first indicationthrough the receiving unit.

In a possible implementation, the processing unit is specificallyconfigured to configure at least two processing resources based on thefirst indication, where one processing resource includes a basebandresource and a fast Fourier transformation FFT, and the at least twoprocessing resources correspond to a same carrier frequency. Thereceiving unit is specifically configured to: receive the downlinksignal from the source base station by using a first processing resourcein the at least two processing resources, and receive the downlinksignal from the target base station by using a second processingresource in the at least two processing resources, where the firstprocessing resource is different from the second processing resource.

In a possible implementation, if the terminal has a carrier aggregationcapability, a bandwidth of a baseband resource included in the firstprocessing resource is the same as a bandwidth of a baseband resourceincluded in the second processing resource, and a size of an FFTcorresponding to the first processing resource is the same as a size ofan FFT corresponding to the second processing resource. Alternatively,if the terminal does not have a carrier aggregation capability, abandwidth of a baseband resource included in the second processingresource is less than or equal to a bandwidth of a baseband resourceincluded in the first processing resource, and a size of an FFTcorresponding to the second processing resource is less than or equal toa size of an FFT corresponding to the first processing resource, wherethe bandwidth of the baseband resource included in the second processingresource is less than or equal to a preset bandwidth threshold.

In a possible implementation, the sending unit is configured to send afirst capability indication to the source base station, where the firstcapability indication is used to indicate that the terminal has anintra-frequency receiving capability.

In a possible implementation, the processing unit is further configuredto not adjust an automatic gain control AGC gain based on the firstindication. Alternatively, the first message further includes a secondindication, and the processing unit is further configured to not adjustan AGC gain based on the second indication.

In a possible implementation, the sending unit is configured to send asecond capability indication to the source base station, where thesecond capability indication is used to indicate that the terminal has acapability of not adjusting the AGC gain.

In a possible implementation, the first indication is further used toindicate a fading margin, and the processing unit is further configuredto set a fixed AGC gain based on the fading margin. Alternatively, thefirst message further includes a third indication, the third indicationis used to indicate a fading margin, and the processing unit is furtherconfigured to set a fixed AGC gain based on the fading margin.

In a possible implementation, the sending unit is configured to send athird capability indication to the source base station, where the thirdcapability indication is used to indicate that the terminal has acapability of setting the fixed AGC gain based on the fading margin.

In a possible implementation, the first message further includes a starttime point, and the processing unit is specifically configured to start,at the start time point, to receive the downlink signals from the sourcebase station and the target base station based on the first indicationthrough the receiving unit.

In a possible implementation, the first message further includes an endtime point, and the processing unit is further configured to stop, atthe end time point, receiving the downlink signals from the source basestation and the target base station. Alternatively, the first messagefurther includes first duration, and the processing unit is furtherconfigured to stop, after the first duration from the start time point,receiving the downlink signals from the source base station and thetarget base station.

In a possible implementation, the first message is a radio resourcecontrol RRC connection reconfiguration message.

In an embodiment, the apparatus 500 may be a base station, or may be achip in a base station. The base station may be configured to implementoperations performed by the source base station in the foregoingembodiments. Specifically, for example, the communications unit 503includes the sending unit and the receiving unit. The processing unit isconfigured to generate a first message, where the first message includesa first indication, and the first indication is used to indicate theterminal to receive downlink signals from the source base station andthe target base station on a same carrier frequency. The sending unit isconfigured to send the first message to the terminal.

In a possible implementation, the receiving unit is configured toreceive a first capability indication from the terminal, where the firstcapability indication is used to indicate that the terminal has anintra-frequency receiving capability.

In a possible implementation, the first indication is further used toindicate the terminal not to adjust an AGC gain. Alternatively, thefirst message further includes a second indication, where the secondindication is used to indicate the terminal not to adjust an AGC gain.

In a possible implementation, the receiving unit is configured toreceive a second capability indication from the terminal, where thesecond capability indication is used to indicate that the terminal has acapability of not adjusting the AGC gain.

In a possible implementation, the source base station receives a thirdcapability indication from the terminal, where the third capabilityindication is used to indicate that the terminal has a capability ofsetting a fixed AGC gain based on a fading margin.

In a possible implementation, the first message further includes a starttime point, so that the terminal may start, at the start time point, toreceive the downlink signals from the source base station and the targetbase station based on the first indication.

In a possible implementation, the first message further includes an endtime point, so that the terminal can stop, at the end time point,receiving the downlink signals from the source base station and thetarget base station. Alternatively, the first message further includesfirst duration, so that after the first duration from the start timepoint, the terminal can stop receiving the downlink signals from thesource base station and the target base station.

In a possible implementation, the first message is a radio resourcecontrol RRC connection reconfiguration message.

For beneficial effects of the foregoing apparatus embodiments, refer torelated descriptions in the foregoing method embodiment. Details are notdescribed herein again.

FIG. 6 is a schematic diagram of an apparatus according to thisapplication. The apparatus may be a terminal or a source base station inan embodiment of this application, or may be a component that can beused for a terminal or a source base station. An apparatus 600 includesa processor 602, a communications interface 603, and a memory 601.Optionally, the apparatus 600 may further include a bus 604. Thecommunications interface 603, the processor 602, and the memory 601 maybe connected to each other through the communication line 604. Thecommunication line 604 may be a peripheral component interconnect (PCI)bus, an extended industry standard architecture (EISA) bus, or the like.The communication line 604 may be classified into an address bus, a databus, a control bus, and the like. For ease of representation, only onethick line is used to represent the bus in FIG. 6, but this does notmean that there is only one bus or only one type of bus.

The processor 602 may be a CPU, a microprocessor, an ASIC, or one ormore integrated circuits configured to control program execution in thesolutions of this application.

The communications interface 603 may be any type of apparatus using atransceiver, and is configured to communicate with another device or acommunications network such as the Ethernet, a radio access network(RAN), a wireless local area network (WLAN), or a wired access network.

The memory 601 may be a read-only memory (ROM) or another type of staticstorage device that can store static information and instructions, or arandom access memory (RAM) or another type of dynamic storage devicethat can store information and instructions, or may be an electricallyerasable programmable read-only memory (EEPROM), a compact discread-only memory (CD-ROM) or another compact disc storage, an opticaldisc storage (including a compact disc, a laser disc, an optical disc, adigital versatile disc, a Blu-ray disc, and the like), a magnetic diskstorage medium or another magnetic storage device, or any other mediumthat can be configured to carry or store expected program code in a formof an instruction or a data structure and that can be accessed by acomputer. However, the memory 601 is not limited thereto. A memory mayexist independently, and is connected to a processor through thecommunication line 604. Alternatively, the memory may be integrated intothe processor.

The memory 601 is configured to store computer-executable instructionsfor executing the solutions in this application, and the processor 602controls the execution. The processor 602 is configured to execute thecomputer-executable instructions stored in the memory 601, to implementthe downlink signal receiving method provided in the foregoingembodiments of this application.

Optionally, the computer-executable instructions in this embodiment ofthis application may also be referred to as application program code.This is not specifically limited in this embodiment of this application.

All or some of the foregoing embodiments may be implemented by usingsoftware, hardware, firmware, or any combination thereof. When softwareis used to implement the embodiments, the embodiments may be implementedcompletely or partially in a form of a computer program product. Thecomputer program product includes one or more computer instructions.When the computer program instructions are loaded and executed on acomputer, the procedure or functions according to the embodiments ofthis application are completely or partially generated. The computer maybe a general-purpose computer, a dedicated computer, a computer network,or another programmable apparatus. The computer instructions may bestored in a computer-readable storage medium or may be transmitted froma computer-readable storage medium to another computer-readable storagemedium. For example, the computer instructions may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, a coaxial cable, anoptical fiber, or a digital subscriber line (DSL)) or wireless (forexample, infrared, radio, or microwave) manner. The computer-readablestorage medium may be any usable medium accessible by a computer, or adata storage device, such as a server or a data center, integrating oneor more usable media. The usable medium may be a magnetic medium (forexample, a floppy disk, a hard disk, or a magnetic tape), an opticalmedium (for example, a DVD), a semiconductor medium (for example, asolid-state drive (SSD)), or the like.

The various illustrative logical units and circuits described in theembodiments of this application may implement or operate the describedfunctions by using a general-purpose processor, a digital signalprocessor, an application-specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or another programmable logicalapparatus, a discrete gate or transistor logic, a discrete hardwarecomponent, or a design of any combination thereof. The general-purposeprocessor may be a microprocessor. Optionally, the general-purposeprocessor may also be any conventional processor, controller,microcontroller, or state machine. The processor may also be implementedby a combination of computing apparatuses, such as a digital signalprocessor and a microprocessor, a plurality of microprocessors, one ormore microprocessors with a digital signal processor core, or any othersimilar configuration.

Steps of the methods or algorithms described in the embodiments of thisapplication may be directly embedded into hardware, a software unitexecuted by a processor, or a combination thereof. The software unit maybe stored in a RAM memory, a flash memory, a ROM memory, an EPROMmemory, an EEPROM memory, a register, a hard disk, a removable magneticdisk, a CD-ROM, or a storage medium of any other form in the art. Forexample, the storage medium may be connected to a processor, so that theprocessor may read information from the storage medium and writeinformation into the storage medium. Alternatively, the storage mediummay further be integrated into a processor. The processor and thestorage medium may be disposed in an ASIC, and the ASIC may be disposedin a terminal. Optionally, the processor and the storage medium mayalternatively be disposed in different components of a terminal.

These computer program instructions may also be loaded onto a computeror another programmable data processing device, so that a series ofoperations and steps are performed on the computer or the anotherprogrammable device, thereby generating computer-implemented processing.Therefore, the instructions executed on the computer or the anotherprogrammable device provide steps for implementing a specific functionin one or more processes in the flowcharts and/or in one or more blocksin the block diagrams.

Although this application is described with reference to specificfeatures and the embodiments thereof, it is clear that variousmodifications and combinations may be made to this application withoutdeparting from the scope of this application. Correspondingly, thespecification and accompanying drawings are merely example descriptionsof this application defined by the appended claims, and is considered asany of or all modifications, variations, combinations or equivalentsthat cover the scope of this application. It is clear that a personskilled in the art can make various modifications and variations to thisapplication without departing from the spirit and scope of thisapplication. This application is intended to cover these modificationsand variations of this application provided that they fall within thescope of protection defined by the following claims and their equivalenttechnologies in this application.

What is claimed is:
 1. A downlink signal receiving method, applied to aprocess in which a terminal is handed over from a source base station toa target base station, wherein the method comprises: receiving, by theterminal, a first message from the source base station, wherein thefirst message comprises a first indication, and the first indication isused to indicate the terminal to receive downlink signals on a samefrequency; and receiving, by the terminal, downlink signals from thesource base station and the target base station based on the firstindication.
 2. The method according to claim 1, wherein the receiving,by the terminal, downlink signals from the source base station and thetarget base station based on the first indication comprises:configuring, by the terminal, at least two processing resources based onthe first indication, wherein one processing resource comprises abaseband resource and a fast fourier transformation (FFT), and the atleast two processing resources correspond to a same carrier frequency;receiving, by the terminal, the downlink signal from the source basestation by using a first processing resource in the at least twoprocessing resources; and receiving, by the terminal, the downlinksignal from the target base station by using a second processingresource in the at least two processing resources, wherein the firstprocessing resource is different from the second processing resource. 3.The method according to claim 2, wherein if the terminal has a carrieraggregation capability, a bandwidth of a baseband resource comprised inthe first processing resource is the same as a bandwidth of a basebandresource comprised in the second processing resource, and a size of anFFT corresponding to the first processing resource is the same as a sizeof an FFT corresponding to the second processing resource; or if theterminal does not have a carrier aggregation capability, a bandwidth ofa baseband resource comprised in the second processing resource is lessthan or equal to a bandwidth of a baseband resource comprised in thefirst processing resource, and a size of an FFT corresponding to thesecond processing resource is less than or equal to a size of an FFTcorresponding to the first processing resource, wherein the bandwidth ofthe baseband resource comprised in the second processing resource isless than or equal to a preset bandwidth threshold.
 4. The methodaccording to claim 1, wherein the method further comprises: sending, bythe terminal, a first capability indication to the source base station,wherein the first capability indication is used to indicate that theterminal has an intra-frequency receiving capability.
 5. The methodaccording to claim 1, wherein the method further comprises: skippingadjusting, by the terminal, an automatic gain control (AGC) gain basedon the first indication; or skipping adjusting, by the terminal, an AGCgain based on a second indication, wherein the first message furthercomprises the second indication.
 6. The method according to claim 5,wherein the method further comprises: sending, by the terminal, a secondcapability indication to the source base station, wherein the secondcapability indication is used to indicate that the terminal has acapability of skipping adjusting the AGC gain.
 7. The method accordingto claim 1, wherein the method further comprises: setting, by theterminal, a fixed AGC gain based on a fading margin, wherein the firstindication is further used to indicate the fading margin; or setting, bythe terminal, a fixed AGC gain based on a fading margin, wherein thefirst message further comprises a third indication, and the thirdindication is used to indicate the fading margin.
 8. A downlink signalreceiving method, applied to a process in which a terminal is handedover from a source base station to a target base station, wherein themethod comprises: generating, by the source base station, a firstmessage, wherein the first message comprises a first indication, and thefirst indication is used to indicate the terminal to receive downlinksignals on a same frequency; and sending, by the source base station,the first message to the terminal.
 9. The method according to claim 8,wherein the method further comprises: receiving, by the source basestation, a first capability indication from the terminal, wherein thefirst capability indication is used to indicate that the terminal has anintra-frequency receiving capability.
 10. The method according to claim8, wherein the first indication is further used to indicate the terminalto skip adjusting an AGC gain; or the first message further comprises asecond indication, wherein the second indication is used to indicate theterminal to skip adjusting an AGC gain.
 11. A terminal, used in aprocess in which the terminal is handed over from a source base stationto a target base station, and comprising: a transceiver, configured toreceive a first message from the source base station, wherein the firstmessage comprises a first indication, and the first indication is usedto indicate the terminal to receive downlink signals from the sourcebase station and the target base station on a same carrier frequency;and a processor, configured to receive the downlink signals from thesource base station and the target base station based on the firstindication through the transceiver.
 12. The terminal according to claim11, wherein the processor is configured to configure at least twoprocessing resources based on the first indication, wherein oneprocessing resource comprises a baseband resource and a fast fouriertransformation (FFT), and the at least two processing resourcescorrespond to a same carrier frequency; and the transceiver isconfigured to: receive the downlink signal from the source base stationby using a first processing resource in the at least two processingresources; and receive the downlink signal from the target base stationby using a second processing resource in the at least two processingresources, wherein the first processing resource is different from thesecond processing resource.
 13. The terminal according to claim 12,wherein if the terminal has a carrier aggregation capability, abandwidth of a baseband resource comprised in the first processingresource is the same as a bandwidth of a baseband resource comprised inthe second processing resource, and a size of an FFT corresponding tothe first processing resource is the same as a size of an FFTcorresponding to the second processing resource; or if the terminal doesnot have a carrier aggregation capability, a bandwidth of a basebandresource comprised in the second processing resource is less than orequal to a bandwidth of a baseband resource comprised in the firstprocessing resource, and a size of an FFT corresponding to the secondprocessing resource is less than or equal to a size of an FFTcorresponding to the first processing resource, wherein the bandwidth ofthe baseband resource comprised in the second processing resource isless than or equal to a preset bandwidth threshold.
 14. The terminalaccording to claim 11, wherein the transceiver is further configured tosend a first capability indication to the source base station, whereinthe first capability indication is used to indicate that the terminalhas an intra-frequency receiving capability.
 15. The terminal accordingto claim 11, wherein the processor is further configured to skipadjusting an automatic gain control (AGC) gain based on the firstindication; or the first message further comprises a second indication,and the processor is further configured to skip adjusting an AGC gainbased on the second indication.
 16. The terminal according to claim 15,wherein the transceiver is further configured to send a secondcapability indication to the source base station, wherein the secondcapability indication is used to indicate that the terminal has acapability of skipping adjusting the AGC gain.
 17. The terminalaccording to claim 11, wherein the first indication is further used toindicate a fading margin, and the processor is further configured to seta fixed AGC gain based on the fading margin; or the first messagefurther comprises a third indication, the third indication is used toindicate a fading margin, and the processor is further configured to seta fixed AGC gain based on the fading margin.
 18. A source base station,used in a process in which a terminal is handed over from the sourcebase station to a target base station, and comprising: a processor,configured to generate a first message, wherein the first messagecomprises a first indication, and the first indication is used toindicate the terminal to receive downlink signals from the source basestation and the target base station on a same carrier frequency; and atransceiver, configured to send the first message to the terminal. 19.The source base station according to claim 18, wherein the transceiveris further configured to receive a first capability indication from theterminal, wherein the first capability indication is used to indicatethat the terminal has an intra-frequency receiving capability.
 20. Thesource base station according to claim 18, wherein the first indicationis further used to indicate the terminal to skip adjusting an AGC gain;or the first message further comprises a second indication, wherein thesecond indication is used to indicate the terminal to skip adjusting anAGC gain.